Deoxycholate Citrate Agar Modified

EMD Cat. No. 1.02896.0500/5000
500 g, 5 kg


Medium proposed by LEIFSON (1935) and modified by HYNES (1942) for the isolation of salmonellae and shigellae.

The culture medium complies with the European Pharmacopeia II.





Mode of Action Preparation
Experimental Procedure and Evaluation Quality Control
Typical Composition (g/liter) Literature
Picture/Image



Typical Composition (g/liter)
 Meat extract 5.0; peptone from meat 5.0; lactose 10.0; sodium thiosulfate 5.4; ammonium iron(III) citrate 1.0; sodium citrate 6.0; sodium deoxycholate 3.0; neutral red 0.02; agar-agar 12.0:

Preparation
 Suspend 47.5 g/liter, cool quickly, pour plates.
 The medium is heat sensitive. Bring to boil with frequent agitation. Do not remelt.
  •   Do not autoclave.
     pH: 7.5 ± 0.2 at 25 °C.
     The plates are clear and reddish-brown.
  •   The prepared culture medium can be stored for 1 week in the refrigerator.

    Experimental Procedure and Evaluation
     Inoculate by spreading the sample or material from an enrichment culture on the surface of the culture medium.
     In view of the strong inhibitory action of LEIFSON Agar, it is advisable to use a less inhibitory selective medium as well, e.g. MaxCONKEY Agar or Deoxycholate Lactose Agar.
     Incubation: 24-48 hours at 35 °C aerobically.
    Appearance of Colonies
         		Microorganisms
    After 18 hours: pale pink to colorless, diameter 1 mm.
     After 48 hours: slightly opaque, often with a central gray dot, diameter approx. 2 mm
         		Salmonella typhosa
    After 18 hours: pale pinkt to colorless, diameter approx.
     1 mm
     After 48 hours: slightly opaque, convex, with a central black dot
         		Salmonella paratyphi B and other H2S-positive salmonellae
    At first colorless, then pale pink (slight lactose degradation).
     After 18 hours: flat, diameter approx. 1 mm.
     After 38 hours: diameter approx 2 mm
         		Shigella sonnei
    As S. sonnei but with a convex centre, often with flat edges
         		Shigella flexneri
    Similar to Salmonella and Shigella, characteristic sweet smell
         		Pseudomonas
    Similar to Salmonella and Shigella, black central dot
         		Proteus vulgaris, most strains of Proteus mirabilis
    Inhibited growth, pink colonies surrounded by turbid precipitation zone, diameter approx. 1-2 mm
         		Escherichia coli
    Inhibited growth, colorless or pink centre, convex, mucoid, opaque, diameter approx. 1-2 mm
         		Enterobacter, Klebsiella


    Quality control

    Test strains
    		 Growth
         		color
         		Colonies Precipitate
         		Black centre
    Escherichia coli ATCC 25922
         		poor / fair
         		red
         		+
         		-
    Klebsiella pneumoniae ATCC 13883
         		good / very good
         		red
         		-
         		-
    Shigella flexneri ATCC 12022
         		fair / very good
         		colorless
         		-
         		-
    Shigella sonnei ATCC 11060
         		fair / very good
         		colorless
         		-
         		-
    Salmonella typhimurium ATCC 14028
         		good / very good
    		colorless
         		-
         		+
    Salmonella enteritidis NCTC 5188
         		good / very good
         		colorless
         		-
         		+
    Proteus mirabilis ATCC 14273
         		good / very good
         		colorless
         		-
         		±
    Staphylococcus aureus ATCC 25923
         		none


    Bacillus cereus ATCC 11778
         		none




    Additives


    EMD Cat. No. Product Pack Size
    1.05287.0500 XLD Agar 500 g
    1.05465.0500 MacCONKEY Agar 500 g


    Literature

    European Pharmacopeia II, Chapter VIII, 10.
     LEIFSON, E.: New culture media based on sodium deoxycholate for the isolation of intestinal pathogens and for the enumeration of colon bacilli in milk and water. - J. Path. Bact., 40; 581-599 (1935).
     HYNES, M.: The isolation of intestinal pathogens by selective media. - J. Path. Bact., 54; 193-207 (1942).


    E.coli



    © 2002 Merck KGaA, Darmstadt, Germany